Induction heating coil



Feb. 4, 1964 R. A. SOMMER INDUCTION HEATING COIL Filed June 29, 1960 VVVVVV T INVENTOR RICHARD A. SOMMER ATTORNEY United States Patent 3,120,596 INDUCTION HEATING CO Richard A. Summer, Parma, Ohio, assignor to The Ohio Crankshaft Company, a corporation of Ohio Filed June 29, 1960, Ser. No. 39,470 8 Claims. (Cl. 219--10.75)

This invention relates to induction coils adapted to heat elongated workpieces and the like, and more particularly to an induction heating coil adapted to heat workpieces of random lengths without overheating their ends.

As is well known, an induction heating coil which extends beyond the end of a workpiece to be heated produces an overheated condition of that end. When the billets or other articles to be heated are all of the same length, a coil may be readily designed with its length substantially equal to that of the article being heated, thereby avoiding any possibility of overheating the ends. When the workpieces are of random lengths, however, a coil of fixed length is entirely unsatisfactory since it must be long enough to heat the longest expected workpiece, meaning that at least one end of workpieces of shorter lengths will be overheated. It is, of course, possible to employ many coils of different lengths to accommodate various sized workpieces; however, this is relatively costly and requires that the workpieces be classified before being inserted into the proper coil. In addition, separate billet handling equipment would be required for each coil.

As a primary object, the present invention provides an induction heating coil assembly in which the portion of the coil which is energized may be varied to suit workpieces of various lengths.

Another object of the invention is to provide an induction heating coil formed from a plurality of axially spaced coil sections which may be selectively energized to suit the length of a workpiece to be heated while at the same time maintaining a relatively constant power density throughout the length of the workpiece.

Still another object of the invention is to provide an induction coil of the type described which requires relatively small transformer means for energizing the spaced coil sections making up the complete coil assembly.

In accordance with the invention, the induction coil assembly for workpieces of random lengths comprises a first coil section having a length adequate for even heating of the shortest workpiece, together with a group of axially spaced coil sections at the ends of the first section, the arrangement being such that after passing through the first section, a workpiece will pass through the remaining sections in succession. The first coil section is adapted for direct connection to a source of electrical energy, while the remaining coil sections are connected in series with the end of the serially-connected coil sections adjacent the first section being connected to one end of an autotransformer. The assembly also includes switches for connecting the other end of the serially-connected sections as well as the junctions between successive ones of said sections to spaced points on the autotransformer. With this arrangement, one or more of the serially-connected coil sections having a portion of a workpiece disposed therein may be energized by closing a selected one of the aforesaid switches, the arrangement being such that those sections extending beyond the end of the workpiece will ice remain de-energized to prevent overheating of the workpiece end.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying single figure drawing which schematically illustrates the invention.

Referring to the drawing, a source of alternating current voltage 10 is adapted for connection through normally open contacts 12 and 14 of switch 16 to the opposite ends of a first induction coil section A. As shown, coil section A forms part of a complete induction coil assembly having a plurality of serially-connected coil sections B, C, D and -E at one end of the coil section A and coaxial therewith. Also connected across alternating current source 10' via contacts 12 and 14 is an autotransforrner :18 which may or may not have a core 20*, depending upon requirements.

The end of coil section B adjacent the first section A is connected via lead 22 to one end of the autotransformer 18-, substantially as shown. The junction between coil sections B and C is connected to point 24 on the autotransformer via switch 26; the junction between sections C and D is connected to point 28 via switch 3%); that between sections D and E is connected to point 32 via. switch 34; and the end of section E farthest removed from the first section A is connected to an end of the autoltransformer via switch 36.

The length of coil section A is adequate for even heating of the shortest workpiece to be heated. Thus, when the shortest workpiece is disposed within section A none of the switches 26, 30, 34 or 36 will be closed so that only coil section A will be energized while all of the following coil sections remain de-energized to prevent overheating of the end of the workpiece. If a workpiece W is inserted into the coil assembly so that its end terminates in coil section C, switch 30 will be closed as shown. This will then energize the coil sections B and C together with coil section A. The remaining coil sections D and E, however, will remain de-energized since both of the switches 34 and 36 are open. In a similar manner, if the end of the workpiece should be within coil section D, then switch 3-4 will be closed while all of the remaining switches remain open in order to energize sections B, C and D in series through the portion of the auto-transformer between its lower end and point 32.

If the lengths of the various coil sections B, C, D and E are equal, then the spacing between the points of connection to the autotransformer 18 will also be equal. Thus, the autotransformer may be divided into four equal sections across which substantially equal voltages will appear. lf switch 26 is closed with the remaining switches open, then the voltage across coil section B will be approximately one-quarter of the total voltage across the autotransformer 18. The coil is divided whereby section B will produce a flux density with this voltage substantially equal to the flux density produced by coil section A so that the power density along the entire length of the billet is the same. If switch 30 should be closed while the other switches remain open, then twice the voltage will appear across coils B and C in series, but since this voltage is now divided, the flux density produced by each coil remains equal to that of section A. Closure of switch 3 34 or 36 will produce the same effect. This is, although the total voltage across the coil sections will increase, that voltage across each individual coil section will remain substantially the same since they are connected in series to produce a constant flux density in the billet regardless of which switch is closed.

It can thus be seen that the invention provides a means for heating billets of various lengths without overheating their ends by merely closing one of the switches 26, 30, 34 or 2:5 determined by the position of the end of the billet Within the coil assembly.

Although-the invention has been shown in connection with a specific embodiment, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

Having thus described my invention, I claim:

1. An induction coil arrangement for heating workpieces of various lengths without overheating their ends comprising, in combination, a first induction coil having a length adequate for even heating to that of the shortest workpiece to be heated, means for connecting said first coil to a source of alternating current voltage, said voltage causing a first current to flow through said first coil, a plurality of axially spaced coil sections at one end of said first coil and coaxial therewith, means connecting said plurality of coil sections in series, an autotransformer adapted for connection to a source of alternating current voltage, a connection between one end of the autotransformer and the end of said serially-connected coil sections adjacent said first coil, and switches adapted to connect the junction between successive ones of said serially-connected coil sections to spaced points on said autotransformer, to impress a voltage across said coil section between said junction and the end of said seriallyconnected coil sections adjacent said first coil, said voltage causing a second current to flow through said coil sections, said first and said second current being substantially equal, the arrangement being such that any single one of said switches may be closed to energize one or more of the serially-connected coil sections having a portion of a workpiece disposed therein.

2. An induction coil arrangement for heating workpieces of various lengths without overheating their ends comprising, in combination, a first induction coil having a length adequate for even heating to that of the shortest workpiece to be heated, means for connecting said first coil to a source of alternating current voltage, a plurality of axially spaced coil sections at one end of said first coil and coaxial therewith, means connecting said plurality of coil sections in series, an autotransformer adapted for connection to a source of alternating current voltage, a connection between one end of the autotransformer and the end of said serially-connected coil sections adjacent said first coil, and switches adapted to connect the junctions between successive ones of serially-connected coil sections to spaced-points on said 'autotransformer with the point'ofconnection to the autotransformer for each junction between successive coil sections being spaced from said one end of the autotransformer in the order of its spacing from said first coil whereby the voltage across each of said coil sections will be substantially equal regardless of which one of the switches is closed.

3. An induction coil arrangement for heating Workpieces of various lengths without overheating their ends comprising, in combination, a first induction coil having a length adequate for even heating to that of the shortest workpiece to be heated, means for connecting said first coil to a source of alternating current voltage, a plurality of axially spaced coil sections at one end of said first coil and coaxial therewith, means connecting said plurality of coil sections in series, a transformer connected across said source of alternating current voltage, output winding means on the transformer, said output winding means divided into winding sections of a number equal to said coil sections, switch means for connecting the one of said axially spaced coil sections immediately adjacent said first coil across one winding section of said winding means, and further switch means for connecting one or more successive ones of said axially spaced coil sections in series with said one axially spaced coil section and across a corresponding number of winding sections of said output winding means.

4-. An induction coil arrangement for heating workpieces of various lengths without overheating their ends comprising, in combination, a first induction coil, means for connecting said first coil to a source of alternating current voltage, a plurality of axially spacedcoil sections at one end of said first coil and coaxial therewith, means connecting said plurality of coil sections in series, transformer means connected across said source of alternating current voltage and having at least one winding thereon, a connection between one end of said winding and the end of said serially-connected coil sections adjacent said first coil, and switches for connecting the junctions between successive ones of said serially-connected coil sections to spaced points on said winding whereby any single one of the switches may be closed to energize one or more of said axially spaced coil sections by a portion of said winding corresponding in length to the length of the coil sections having a portion of a workpiece to be heated disposed therein.

5. An induction coil arrangement for heating workpieces of various lengths without overheating their ends comprising, in combination, a first induction coil having a length adequate for even heating to that of the shortest workpiece to be heated, means for connecting said first coil to a source of alternating current voltage to give a predetermined current in said first coil, a plurality of axially spaced coil sections at one end of said first coil and coaxial therewith, means connecting said plurality of coil sections in series, an autotransformer adapted for-connection to a source of alternating current voltage, a connection between one end of the autotransiormer and the end of said serially-connected coil sections adjacent said first coil, switch means connecting the other end of the autotransformer to the end of said seriallyconnected coil sections farthest removed from said first coil, and switch means adapted to connect the junctions between successive ones of said serially-connected coil sections to different portions of said autotransformer defined by spaced points on said autotransformer between its opposite ends, the portions of said autotransformer connected to said coil sections having a length to give a current in said coil section substantially equal to the current in said first coil.

6. The combination claimed in claim 5 wherein the connection of any one of said junctions to the autotransformer by closure of a single one of said switch'means will energize each of the axially spaced coil sections preceding that junction in the path of travel of a workpiece through the induction coil arrangement.

7. An'induction coil arrangement for heating workpieces of various lengths without overheating their ends comprising, in combination, a first induction coil having a length adequate for even heating to that of the shortest workpiece to be heated, means connecting said first coil to a source of alternating current voltage, said voltage causing a first current to flow through said first coil, a plurality of axially spaced coil sections at one end of said first coil and coaxial therewith, said coil sections connected in series by a number of taps between adjacent coil sections, an autotransformer having an equal number of taps on its secondary winding, said autotransformer connected to a source of alternating current voltage, one end of said secondary winding connected to the end of said coil sections adjacent said first coil, a plurallty of switch means connecting said taps on said secondary winding to said tapsbetwe'en said coil sections, the"volt--' age between taps on said autotransfornier being substantially equal and the distance between taps of said coil sections being substantially equal, said switch means selectively closed to energize a given number of coil sections by a voltage proportional to the combined length of the coil sections.

8. An induction coil arrangement for heating workpieces of various lengths without overheating their ends comprising, in combination, a first induction coil having a length adequate for even heating of the shortest workpiece to be heated, means for connecting said first coil onto a source of alternating current voltage, a plurality of axially spaced coil sections at one end of said first coil and coaxial therewith, and means for energizing a preselected number of said coil sections to define a second coil of given length extending axially from said first coil with a voltage having a magnitude equal to the voltage of said source times the ratio of the second coil length to the total length of the coil sections.

References Cited in the file of this patent UNITED STATES PATENTS 1,791,934 Northrup Feb. 10, 1931 2,720,577 Lackner Oct. 11, 1955 2,839,652 Dreyfus June 17, 1958 2,909,585 Tudbury u Oct. 20, 1959 

8. AN INDUCTION COIL ARRANGEMENT FOR HEATING WORKPIECES OF VARIOUS LENGTHS WITHOUT OVERHEATING THEIR ENDS COMPRISING, IN COMBINATION, A FIRST INDUCTION COIL HAVING A LENGTH ADEQUATE FOR EVEN HEATING OF THE SHORTEST WORKPIECE TO BE HEATED, MEANS FOR CONNECTING SAID FIRST COIL ONTO A SOURCE OF ALTERNATING CURRENT VOLTAGE, A PLURALITY OF AXIALLY SPACED COIL SECTIONS AT ONE END OF SAID FIRST COIL AND COAXIALY THEREWITH, AND MEANS FOR ENERGIZING A PRESELECTED NUMBER OF SAID COIL SECTIONS TO DEFINE A SECOND COIL OF GIVEN LENGTH EXTENDING AXIALLY FROM SAID FIRST COIL WITH A VOLTAGE HAVING A MAGNITUDE EQUAL TO THE VOLTAGE OF SAID SOURCE TIMES THE RATIO OF THE SECOND COIL LENGTH TO THE TOTAL LENGTH OF THE COIL SECTIONS. 